The present invention relates to air ventilation and an improved air ventilation system which includes both heat recovery and dehumidification.
ANSI/ASHRAE Standard 62-1989 was established to address the need for increased ventilation of buildings due to poor indoor air quality. Increased levels of contaminants from humans, fuel burning appliances, building materials and furnishings have resulted from the current construction practices which produce tighter, low leakage buildings. For example, volatile organic compounds (VOCs) such as formaldehyde have been identified which with continued exposure can cause illness. Recommended ventilation rates range from about 0.3 air changes per hour to over 1.0 air changes per hour. The actual level of recommended outdoor air intake depends on the use, size and occupancy of the building.
Indoor air quality is also affected by the presence of living organisms in the circulated air. Bacteria, mold and mildew, for example, thrive when damp conditions exist in the building and air ducts. For this reason, reduction of humidity levels is not only a comfort concern but also a health concern. Homeowners can reduce their exposure to harmful bacteria, mold and mildew by regulating the humidity level within their homes.
Homeowners also are becoming more aware of the importance of including air ventilation systems within their homes. Therefore, there exists a need for smaller, less complex, less expensive ventilation and dehumidification systems that are appropriate for residential use.
The present system relates to devices that combine ventilation and dehumidification. One type of such devices uses sorptive wheels that transfer heat or moisture from one air stream to another. Although the art is cognizant of xe2x80x9cunitaryxe2x80x9d sorptive wheels that are able to exchange both heat and moisture, the typical ventilating/dehumidifying device uses multiple wheels; usually at least one wheel is primarily a heat exchanger and at least one other wheel is primarily a moisture exchanger. The use of multiple wheels is likely motivated by the fact that a single wheel, operating always at a predetermined speed, is unable to transfer both heat and moisture at maximum efficiency. The shortfall in efficiency of the single wheel arises from the fact that heat transfer which is essential in the ventilating process, is maximized by rotating the wheel at much higher speeds than the speeds required to optimize moisture transfer, which is essential in the dehumidifying process.
The present invention is a device that allows the use of a single sorptive wheel while performing the ventilation and dehumidification functions at optimal levels. In the device, optimization of heat or moisture transfer is achieved by varying the speed of the sorptive wheel. In dehumidification mode, the wheel is rotated slowly, while in ventilation mode the wheel is rotated much faster.
U.S. Pat. No. 5,148,374 discloses a desiccant space conditioning system using multiple sorptive wheels. Although the invention discloses modifying the speeds of the wheels to optimize the effectiveness of the system for various fluid flow rates, temperatures, and water vapor concentrations, the invention does not teach the varying the speed of a single wheel in order to achieve an entirely different function with the same wheel.
U.S. Pat. No. 4,769,053 discloses an air treatment system utilizing a sorptive wheel that is capable of transferring both heat and moisture with high efficiency. The wheel incorporates layers of heat exchanger material with layers of moisture transfer (desiccant) material. However, the invention is concerned with constructing a wheel that will exchange heat and moisture given the constraint of a constant speed, not in varying the speed of the wheel to accomplish the two functions.
U.S. Pat. No. 4,180,985 discloses an improved method and apparatus for air conditioning, using a refrigeration system. The disclosed method and apparatus provide for a refrigerant based air conditioning system to be equipped with a regenerable desiccant for contacting moist feed air prior to passing the feed air across evaporator coils of the system. The desiccant removes a substantial portion of moisture from the feed air, thereby improving the efficiency of the air conditioning system. The desiccant material is regenerated by utilizing waste heat that is removed from the condenser of the air conditioning system.
U.S. Pat. No. 5,179,998 discloses a heat recovery ventilating dehumidifier which is a multifunction device for the treatment of air. The invention, however, uses compression and refrigeration in order to achieve dehumidification.
In accordance with the present invention there is provided a ventilation and dehumidification system for ventilating fresh air to a conditioned space. The system is comprised of a unitary heat transfer desiccant wheel for dehumidifying incoming air by exchanging moisture from an inflow current of air with an outflow current of air. In addition the unitary heat recovery wheel is able to transfer heat between the two air currents when the wheel is spun at a faster speed. The unitary heat transfer desiccant wheel is both regenerated and defrosted by a regenerative heater which is placed to heat the outflow current of air before the outflow current passes through the unitary heat transfer desiccant wheel. A multi-speed or variable speed motor spins the unitary heat transfer desiccant wheel at a slow speed to accomplish more dehumidification, and at a fast speed to accomplish more heat recovery. The system includes at least two blowers in order to motivate the inflow and outflow currents of air. The blowers can be arranged so as to create an air pressure differential between the inflow chamber and the outflow chamber so that any leakage of air between the two chambers will occur from the inflow chamber to the outflow chamber.